Drivetrain and method for providing a supply to a compressed air system

ABSTRACT

The invention relates to a drivetrain, in particular motor vehicle drivetrain, 
     with a combustion engine having a drive output shaft and which produces a hot exhaust-gas flow; 
     with a turbocompound system comprising: 
     an exhaust-gas turbine which is arranged in the exhaust-gas flow such that it can be impinged upon by exhaust gas and which converts exhaust-gas energy into propulsive energy, wherein the exhaust-gas turbine is drive-connected, or can be switched so as to be drive-connected, to the output shaft of the internal combustion engine and also drives a turbocompressor or positive-displacement compressor by means of which the internal combustion engine is charged on the fresh-air side; 
     with a compressed air system, comprising: 
     an air compressor which can be driven by means of the combustion engine or an additional motor and which feeds compressed air into at least one compressed-air circuit or a compressed-air line. 
     The invention is characterised by 
     the fact that the air compressor can be charged by means of the turbocompressor or positive-displacement compressor of the turbocompound system, wherein air compressed by the turbocompressor or positive-displacement compressor is supplied to the air compressor on its intake side.

The present invention relates to a drivetrain, in particular a motor vehicle drivetrain with a compressed air system and also a method for supplying a compressed air system, in particular of a motor vehicle compressed air system.

It is known for provision to be made for a compressed air system in motor vehicles, particularly utility vehicles, referring in the present case not only to road vehicles but also to rail vehicles, which holds compressed air in readiness for the various vehicle assemblies. As a rule, these assemblies are integrated in compressed air circuits, which need to be re-filled with compressed air from time to time due to the consumption of compressed air by the assemblies and leakage. For instance, compressed air is required for the brakes of a utility vehicle on the road or of a rail vehicle on rail lines. Due to the high safety relevance of the braking system it is necessary to have compressed air of sufficient pressure and in sufficient quantity at one's disposal. The present invention relates in particular to a vehicle with such a brake compressed air circuit.

Patent application publication DE 34 35 732 A1 proposes charging an air compressor in the form of a centrifugal compressor powered by a combustion engine by means of a turbocompressor. To this end, the turbocompressor, also known as a radial compressor or precompressor, compresses fresh air that it supplies to the air compressor via a cooler on the intake side. Thanks to this pre-compression or supercharging, the air compressor itself can be designed to be small as on the one hand it has to take in a smaller volume of fresh air and on the other the pressure ratio between the pressurised side and the intake side needs to be less. In the aforementioned document the turbocompressor is powered by means of an exhaust turbine arranged in the exhaust gas stream of the internal combustion engine downstream from the turbine of an exhaust turbocharger, with the exhaust turbocharger, as is already known, serving to charge the combustion engine.

Further publications describing charged air compressors in the form of displacement machines are DE 1 231 951 and DE 35 10 492 C2.

Although smaller air compressors should be able to be used with the known drivetrains, in practice it has been shown that these compressors are not able to provide sufficient compressed air in certain operational states so that in contrast with the aforementioned patent documents one must resort in practice to comparatively large air compressors, which are actually designed for systems without compressor precharging.

The aim of the present invention is to disclose a drivetrain with a compressed air system accordingly and a method for supplying a compressed air system with compressed air, which makes it possible to supply sufficient compressed air in all prevailing operating conditions, even with a comparatively small air compressor.

The aim of the invention is fulfilled by a drivetrain and a method according to the independent claims. The dependent claims provide advantageous and particularly functional designs of invention.

According to the invention, a turbocompound system and a compressed air system of a drivetrain combine together in such a way that the air compressor of the compressed air system is charged by means of a turbocompressor or displacement compressor of the turbocompound system. This means that the air compressor is supplied with compressed air on its intake side by means of the turbocompressor or displacement compressor, ensuring a sufficient charge even in operational states with comparatively little exhaust energy and/or with a comparatively small exhaust gas stream. Conventional systems with charged compressors exhibit operational states, namely at low speed and/or minimal combustion engine output, in which only a low exhaust gas stream with low energy impinges upon the exhaust turbine driving the turbocompressor. This results in low precompression accordingly, making sufficient charging by means of the turbocompressor impossible. According to the invention, the drive output of the combustion motor can now be used via the drive connection of the turbocompound system to drive the turbocompressor or displacement compressor to precharge the air compressor with the requisite power, even in operational states with low exhaust flow and/or with low exhaust energy.

Specifically, the drivetrain according to the invention, designed in particular as a motor vehicle drivetrain, has a turbocompound system in addition to a combustion engine, said system comprising an exhaust turbine to be impinged upon by exhaust gas and arranged in the exhaust gas stream of the combustion engine and a turbocompressor or displacement compressor driven by the exhaust turbine. The exhaust turbine converts exhaust energy into drive energy and can be drive-connected with the drive shaft of the combustion engine or can be connected to one. In particular, provision is made in the drive connection for a hydrodynamic coupling, in particular a variable control hydrodynamic coupling. In addition or alternatively, it is possible to design the exhaust-gas power-recovery turbine to be governed with respect to its power output.

The turbocompressor or displacement compressor serves to charge the combustion engine, that means to compress fresh air that is fed to the combustion engine for combustion together with fuel. A displacement compressor that comes into consideration is for instance the Roots supercharger. Other displacement compressors are possible, with only rotating screw compressors or gear wheel pumps being given as examples.

The drivetrain according to the invention is also provided with a compressed air system comprising an air compressor that can be actuated by means of the internal combustion engine and/or an additional engine in order to feed compressed air into at least one compressed air circuit. Provision can be made for example for a compressed air brake circuit. In addition or as an alternative to the compressed air circuit, provision can also be made for a simple compressed air line into which the air compressor feeds compressed air. One embodiment of such a compressed air line will be shown with reference to the figure.

According to the invention, the air compressor can be charged by means of a turbocompressor or displacement compressor of the turbocompound system. This means that compressed air compressed by the turbocompressor/displacement compressor can be fed to the air compressor on its intake side such that the turbocompressor/displacement compressor works as a supercharger for the air compressor.

In particular, the air compressor is developed as a piston-type compressor, for example as a single stage or two-stage piston compressor.

As a rule, the compressed air system is provided with an accumulator into which the air compressor conveys compressed air, with a plurality of compressed air circuits being supplied advantageously by means of the accumulator.

According to one embodiment, the air compressor can be driven by a motor by means of the compressor converting the compression energy from the compressed air fed into it into drive energy, for example from the accumulator, one of the compressed air circuits or the turbocompressor/displacement compressor. It is particularly advantageous when the air compressor is arranged in a drive connection with the drive shaft of the combustion engine or such a connection can be switched to transmit propulsive power into the drivetrain.

According to an advantageous embodiment, provision is made for a connecting line between the compressed air system, in particular its compressed air reservoir, and the fresh air side of the combustion engine. The compressed air from the compressed air system and/or the compressed air reservoir can be supplied to the combustion engine on the fresh air side selectively through the connecting line as an additional media flow.

For instance, a connecting line can discharge in the direction of flow downstream from a turbocompressor of a turbocharger, for which provision is made in addition to the turbocompound, in particular after a downstream air cooler in the fresh air flow on the fresh air side of the combustion engine.

In accordance with the method according to the invention for supplying a compressed air system, in particular in a drivetrain according to the invention, the following steps are executed:

-   -   an air compressor is powered by means of a combustion engine         generating an exhaust flow or by means of a motor for which         additional provision is made;     -   air is compressed by means of an air compressor and fed into at         least one compressed air circuit and/or one compressed air line;     -   a turbocompressor or displacement compressor, which compresses         fresh air that is supplied to the combustion engine on the fresh         air side, is powered by means of an exhaust turbine arranged in         the exhaust gas stream;     -   furthermore, compressed fresh air is fed into the air compressor         on the intake side by means of the turbocompressor/displacement         compressor; wherein     -   in operational states where the exhaust gas stream being fed         into the exhaust turbine has a comparatively low energy content,         the exhaust turbine and/or the turbocompressor/displacement         compressor is driven by means of a combustion engine.

The invention shall be described in an exemplary manner on the basis of one example embodiment and the figure.

FIG. 1 shows a schematic representation of a drivetrain with a combustion engine 1, provided with a drive shaft 1.1. The combustion engine 1 generates an exhaust gas stream 2, which is first conveyed through the turbocharger turbine 10 of an exhaust turbocharger 9 and then through the exhaust turbine 3 of a turbocompound system 15.

The turbocharger turbine 10 drives a turbocharger compressor 11, for example as shown, via a common shaft bearing the turbocharger turbine 10 and the turbocharger compressor 11 and/or their runners. The turbocharger compressor 11 is arranged in a fresh air stream 12 conveyed to the combustion engine 1. Said turbocharger compressor compresses the fresh air stream using the drive input from the turbocharger turbine 10, specifically in the direction of flow of the fresh air stream 12 downstream from a turbocompressor 4 of the turbocompound system driven by means of the exhaust turbine 3. The exhaust turbine 3 and the turbocompressor 4 and/or their runners can also be non-rotationally connected to each other as shown, for example by means of a common shaft.

After the fresh air stream 12 has been compressed by the turbocompressor 4 and the turbocharger compressor 11, it is conveyed through an intercooler 16 and finally supplied on the fresh air side to the combustion engine 1. The intercooler 16 can for instance be a component of the vehicle cooling system and be arranged sequentially in terms of a heat exchanger 17 for the vehicle cooling circuit 18, comprising a cooling water pump 19 with respect to a cooling air stream 22 conveyed through the coolers 16 and 17. The output shaft 1.1 of the combustion engine drives an air compressor 6 of a compressed air system 5. The air compressor 6, shown in the present case as a two-stage compressor with two cylinders, compresses the fresh air conveyed to it and feeds this into a compressed air reservoir 7 of the compressed air system; said air compressor could also be developed as a single stage compressor with one cylinder as a result of the supercharging according to the invention. In the present case, four compressed air circuits K1-K4 are filled with compressed air from the compressed air reservoir 7, with the upstream protection valve 23 preventing the pressure from falling in other compressed air circuits if the pressure in one of the compressed air circuits K1-K4 drops. In this way, the protection valve 23 separates the compressed air circuits K1-K4 from each other in a pressure-tight manner. One of the compressed air circuits is for example a compressed air brake circuit. The compressed air reservoir 7 could also be dispensed with or provision could be made in addition for at least another compressed air reservoir. Provision could also be made for a further compressed air circuit in place of the compressed air reservoir 7.

According to a possible, but not compelling detail of the embodiment represented, compressed air can be fed to the fresh air side of the combustion motor 1 by means of the compressed air reservoir 7, particularly in an advantageous manner, via a connecting line 13, which for example has its outlet in the direction of flow downstream from the turbocompressor 4 and the turbocharger compressor 11 and in particular behind the intercooler 16. In the case of the embodiment shown, not only the connecting line 13, but also the line 24 conducting the fresh air stream from the intercooler 16 each have a control element, in particular an electromechanically activated control flap 25, which prevents a return flow of compressed air from the compressed air reservoir 7 toward the intercooler 16, making it possible for compressed air from the compressed air reservoir 7 to be selectively supplied to the fresh air side of the combustion engine 1. Of course, it is also possible to arrange the outlet of the connecting line 13 at another point in the fresh air stream 12, for instance ahead of the intercooler 16, between the turbocompressor 4 and the turbocharger compressor 11 or ahead of the turbocompressor 4. However, the position indicated has proven to be advantageous as the compressed air from the compressed air reservoir 7 does not generally need to be cooled and supercharging is optimised by the embodiment shown.

Of course, it would also be possible to run the connecting line 13 between the compressed air system 5 or the compressed air reservoir 7 and the fresh air side of the combustion engine 1 via the protection valve 23 or connect it to one of the compressed air circuits K1 to K4.

Provision is made for a branch 20 in the fresh air stream 12 downstream from the turbocharged turbine 11 and ahead of the intercooler 16, with fresh air capable of being diverted from the fresh air stream 12 via said branch and selectively guided to the air compressor 6 for precharging the same via an intercooler line 8, in particular having a valve 21. For example, as shown, the supercharged fresh air stream can be mixed with a compressed air system fresh air stream 26. Alternatively, it is also possible to dispense with the compressed air system fresh air stream 26 and to compress all the fresh air supplied to the air compressor 6 by means of the turbocompressor 4 and in particular additionally by means of the turbocharger compressor 11.

Although the branch 20 shown in the present case is depicted upstream of the intercooler 16 and downstream from the turbocharger turbine 11, another position could be chosen, for example between the turbocompressor 4 and the turbocharger compressor 11 or after the intercooler 16 in the direction of flow. In the latter case, relatively cooler air would be supplied to the air compressor 6, something that can be advantageous with respect to the heat generated by compression in the air compressor.

The drive output generated from the exhaust gas stream 2 by means of the exhaust turbine 3 can be conveyed via the turbocompound system 15 of the drive shaft 1.1 of the combustion engine. Furthermore, if necessary due to unfavourable states in the exhaust stream, the drive output of the combustion engine 1 can be conveyed via the drive shaft 1.1 of the exhaust turbine 3 and therefore to the turbocompressor 4 connected non-rotationally to said drive shaft in order to drive the exhaust turbine 4. In this way, sufficient drive output is available to charge the air compressor 6 even during turbo lag operational states.

In the drive connection between the exhaust turbine 3 and the output shaft 1.1 of the internal combustion engine 1, which is developed in particular as a crankshaft, a hydrodynamic coupling 14 is arranged, which can be developed as a variable control coupling as outlined. A variable control hydrodynamic coupling 14 includes not only couplings with a volumetric efficiency control, but also couplings, the circulatory flow of which can be interrupted by the working fluid in the work space by means of an orifice plate in order to reduce the output transmitted onto the turbine wheel from the impeller.

Alternatively or additionally, it is also possible to develop the exhaust turbine 3 and/or the turbocompressor 4 with a variable control in order to control either the output transmitted between the exhaust turbine 3 and the output shaft 1.1 of the internal combustion engine 1 or to control the compressor output of the turbocompressor 4. The turbine and/or the compressor can also be controlled by opening and closing (partially or completely) a bypass or a plurality of bypasses.

Not only is it possible to charge the air compressor 6 in all operational states sufficiently with the drivetrain represented, but also to convey an additional stream of compressed air to the fresh air side of the combustion engine 1 from the compressed air reservoir 7 or if required also from one of the compressed air circuits K1-K4 in order to increase the output of the combustion engine, particularly when the vehicle is moving off from a standstill. Furthermore, although this is not shown, provision can be made to convey compressed air from the compressed air system 5, in particular from the compressed air reservoir 7, to the exhaust gas stream 2 of the combustion engine in order to modify the exhaust gas temperature, in particular to reduce it.

Also, the air compressor 6 can be actuated during vehicle braking operations in order to exert a braking action on the drive shaft 1.1 of the combustion engine 1 and at the same time to temporarily store the generated energy in the compressed air reservoir 7 in the form of compressed air. If required, the compressed air can also be released into the environment through an outlet valve when the compressed air reservoir 7 is full. Alternatively or in addition, provision is also to be made in the exhaust gas stream 2 for a so-called ‘waste gate’, from which exhaust gas can be released before it is conveyed to the turbocharger turbine 10 or the exhaust turbine 3. 

1. Drivetrain, in particular motor vehicle drivetrain, having a combustion engine having a drive shaft and generating a hot exhaust gas stream; having a turbocompound system comprising: an exhaust gas turbine, arranged in the exhaust gas stream to be impinged upon by exhaust gas and converting exhaust energy into drive energy, with the exhaust gas turbine drive-connected via a hydrodynamic coupling to the drive shaft of the combustion engine or able to be switched into one and also driving a turbocompressor or displacement compressor by means of which the combustion engine is supercharged on the fresh air side; having a compressed air system comprising: an air compressor, which can be driven by means of a combustion engine or an additional engine and which feeds its compressed air into at least one compressed air circuit or into a compressed air line; wherein the air compressor can be supercharged by means of the turbocompressor or displacement compressor of the turbocompound system, with the air compressed by the turbocompressor or displacement compressor being supplied to the air compressor on the intake side.
 2. Drivetrain according to claim 1, wherein the air compressor is developed as a piston-type compressor.
 3. Drivetrain according to claim 1, wherein the compressed air system is provided with a compressed air reservoir into which the air compressor conveys compressed air and provision is made in particular for a plurality of different compressed air circuits, with at least one compressed air circuit being developed as a compressed air brake circuit for vehicle brakes.
 4. Drivetrain according to claim 1, wherein the air compressor is drive-connected to the drive shaft of the combustion engine or can be switched into one and can be motor driven to feed drive output.
 5. Drivetrain according to claim 1, wherein provision is made for a connecting line for compressed air between the compressed air system, in particular its compressed air reservoir, and the fresh air side of the combustion engine, through which compressed air from the compressed air system can be selectively conveyed to the fresh air side of the combustion engine for supercharging.
 6. Drivetrain according to claim 1, wherein in addition to the turbocompound system provision is made for a turbocharger, comprising a turbocharger turbine in the exhaust gas stream of the combustion engine, in particular in the direction of flow of the exhaust gas upstream from the exhaust turbine of the turbocompound system, and a turbocharger compressor in a fresh air stream conveyed to the combustion engine, in particular in the direction of flow of fresh air downstream from the turbocompressor or the displacement compressor of the turbocompound system, with the turbocharger compressor being driven by the turbocharger turbine, in particular arranged non-rotatably on a common shaft.
 7. Drivetrain according to claim 6, wherein the air compressor can be charged by means of the turbocompressor or the displacement compressor of the turbocompound system and of the turbocharger compressor, with an intercooler line, in particular that branches off from the fresh air stream in the direction of flow after the two compressors—turbocompressor/turbocharger compressor and turbocharger compressor—and discharges on the intake side of the air compressor.
 8. Method for supplying a compressed air system, in particular a motor vehicle compressed air system, involving the following steps: an air compressor is driven by means of a combustion engine that generates an exhaust gas stream or by means of a motor for which additional provision is made; the air is compressed by means of an air compressor and fed into at least one compressed air circuit and/or one compressed air line; a turbocompressor or displacement compressor is driven by means of an exhaust turbine arranged in the exhaust gas stream, with said turbocompressor or displacement compressor conveying fresh air to the combustion engine on the fresh air side; compressed fresh air is supplied to the air compressor on the intake side by means of the turbocompressor or the displacement compressor; wherein in operational states where the exhaust gas stream being fed into the exhaust turbine has a comparatively low energy content, the exhaust turbine and/or the turbocompressor or displacement compressor is driven.
 9. Method according to claim 8, wherein the exhaust turbine and/or turbocompressor or displacement compressor is driven by means of a drive connection from a drive shaft of the combustion engine via a hydrodynamic coupling to a shaft bearing the exhaust turbine and/or the turbocompressor.
 10. Drivetrain according to claim 2, wherein the compressed air system is provided with a compressed air reservoir into which the air compressor conveys compressed air and provision is made in particular for a plurality of different compressed air circuits, with at least one compressed air circuit being developed as a compressed air brake circuit for vehicle brakes.
 11. Drivetrain according to claim 2, wherein the air compressor is drive-connected to the drive shaft of the combustion engine or can be switched into one and can be motor driven to feed drive output.
 12. Drivetrain according to claim 3, wherein the air compressor is drive-connected to the drive shaft of the combustion engine or can be switched into one and can be motor driven to feed drive output.
 13. Drivetrain according to claim 2, wherein provision is made for a connecting line for compressed air between the compressed air system, in particular its compressed air reservoir, and the fresh air side of the combustion engine, through which compressed air from the compressed air system can be selectively conveyed to the fresh air side of the combustion engine for supercharging.
 14. Drivetrain according to claim 3, wherein provision is made for a connecting line for compressed air between the compressed air system, in particular its compressed air reservoir, and the fresh air side of the combustion engine, through which compressed air from the compressed air system can be selectively conveyed to the fresh air side of the combustion engine for supercharging.
 15. Drivetrain according to claim 4, wherein provision is made for a connecting line for compressed air between the compressed air system, in particular its compressed air reservoir, and the fresh air side of the combustion engine, through which compressed air from the compressed air system can be selectively conveyed to the fresh air side of the combustion engine for supercharging.
 16. Drivetrain according to claim 2, wherein in addition to the turbocompound system provision is made for a turbocharger, comprising a turbocharger turbine in the exhaust gas stream of the combustion engine, in particular in the direction of flow of the exhaust gas upstream from the exhaust turbine of the turbocompound system, and a turbocharger compressor in a fresh air stream conveyed to the combustion engine, in particular in the direction of flow of fresh air downstream from the turbocompressor or the displacement compressor of the turbocompound system, with the turbocharger compressor being driven by the turbocharger turbine, in particular arranged non-rotatably on a common shaft.
 17. Drivetrain according to claim 3, wherein in addition to the turbocompound system provision is made for a turbocharger, comprising a turbocharger turbine in the exhaust gas stream of the combustion engine, in particular in the direction of flow of the exhaust gas upstream from the exhaust turbine of the turbocompound system, and a turbocharger compressor in a fresh air stream conveyed to the combustion engine, in particular in the direction of flow of fresh air downstream from the turbocompressor or the displacement compressor of the turbocompound system, with the turbocharger compressor being driven by the turbocharger turbine, in particular arranged non-rotatably on a common shaft.
 18. Drivetrain according to claim 4, wherein in addition to the turbocompound system provision is made for a turbocharger, comprising a turbocharger turbine in the exhaust gas stream of the combustion engine, in particular in the direction of flow of the exhaust gas upstream from the exhaust turbine of the turbocompound system, and a turbocharger compressor in a fresh air stream conveyed to the combustion engine, in particular in the direction of flow of fresh air downstream from the turbocompressor or the displacement compressor of the turbocompound system, with the turbocharger compressor being driven by the turbocharger turbine, in particular arranged non-rotatably on a common shaft.
 19. Drivetrain according to claim 5, wherein in addition to the turbocompound system provision is made for a turbocharger, comprising a turbocharger turbine in the exhaust gas stream of the combustion engine, in particular in the direction of flow of the exhaust gas upstream from the exhaust turbine of the turbocompound system, and a turbocharger compressor in a fresh air stream conveyed to the combustion engine, in particular in the direction of flow of fresh air downstream from the turbocompressor or the displacement compressor of the turbocompound system, with the turbocharger compressor being driven by the turbocharger turbine, in particular arranged non-rotatably on a common shaft. 